<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
    <style>
      body {
        margin: 0;
        padding: 0;
      }
      .nav {
        width: 900px;
        height: 60px;
        margin: 10px auto;
      }

      ul {
        list-style: none;
        margin: 0;
        padding: 0;
      }

      .nav ul li{
        float: left;
        width: 180px;
        height: 60px;
        text-align: center;
        line-height: 60px;
        background-color: darkcyan;
      }

      .nav ul li:hover{
        background-color: teal;
        font-weight: bold;
      }

      .nav ul li:hover:nth-child(2) .samt-nav{
        display: block;
      }

      .nav ul li a{
        text-decoration: none;
        color: white;
      }

      .samt-nav{
        display: none;
      }
    </style>
  </head>
  <body>
    <div class="nav">
      <ul class="nav-list">
        <li>
          <a href="#">首页</a>
        </li>
        <li>
          <a href="#">SAMTC</a>
          <ul class="samt-nav">
            <li>
              <a href="#">S钢</a>
            </li>
            <li>
              <a href="#">A铝</a>
            </li>
            <li>
              <a href="#">M镁</a>
            </li>
            <li>
              <a href="#">T钛</a>
            </li>
          </ul>
        </li>
        <li>
          <a href="#">产品</a>
        </li>
        <li>
          <a href="#">服务</a>
        </li>
        <li>
          <a href="#">联系我们</a>
        </li>
      </ul>
    </div>

    <div class="banner"></div>
  </body>
</html>
